The primary congenital bleeding disorders are hemophilia A and B, which affect approximately 1 in 5,000 males and von Willebrand's Disease which affects 1 in 100 men and women. Several plasma proteins called factors are necessary for normal blood clotting. Persons with hemophilia are either missing a particular factor in their blood that is essential to the clotting process or the protein is present but does not work. Without this factor, bleeding into muscles, joints, and internal organs often occurs without any noticeable trauma. The treatment of a bleeding episode involves the replacement of the missing protein through intravenous administration of factor concentrate which is derived from, or contains components of human blood. The frequent bleeding and the necessary intravenous administration of blood products to control the bleeding are responsible for the two most severe complications of hemophilia: 1) development of chronic joint disease from repeated bleeding into major joints; and 2) infection with viral, blood-borne disease such as hepatitis and HIV. About three-fourths of all persons with hemophilia in the US receive some of their treatment from federally-sponsored, specialized hemophilia treatment centers (HTCs). The Center for Disease Control and Prevention (CDC) provides support to these treatment centers for programs designed to prevent complications of hemophilia. The Universal Data and Serum Specimen Collection System will extend CDC's collaboration with the HTCs by assisting with the analysis of a uniform set of clinical data which are used to monitor the extent of complications in congenital bleeding disorders in the US. Specific measurements will be used to evaluate the degree of joint disease. In addition, serum will be tested for the presence of blood borne pathogens. The remainder of each serum specimen will be used by the CDC to establish a serum bank for possible future use in evaluating the safety of blood products. Information from this system will be used to assess the safety of the blood supply and to develop and monitor the effectiveness of interventions designed to address the mandate from congress which is to reduce or prevent the complications of hemophilia.